Preliminary Results from a Towed Streamer Controlled Source Electromagnetic Survey for Groundwater over the New England Continental Shelf

Abstract:

Groundwater on continental shelves is a new frontier in hydrological science that has important links to environmental and climate change. A modeling study suggests that as much as 1300 km³ of fresh water could be trapped offshore New England. A towed streamer controlled source electromagnetic (CSEM) system was designed, constructed and tested that is aimed at delineating offshore groundwater, building on experience in the petroleum industry using a similar technology. CSEM is preferentially sensitive to resistive bodies, which include fresh water. During the course of an 8 day test cruise in August 2019, more than 700 km of data were collected over a region extending from the east end of Martha’s Vineyard to offshore Long Island and from coastal waters to the edge of the continental shelf. The towed streamer CSEM system comprises a 1 km long receive streamer towed at half of the water depth and a 200 m long transmit dipole towed near the surface. The transmit streamer is powered by a 250 A source producing a bespoke waveform between 0.1-10 Hz. Data are available in real time via optical fibers in the streamer cable. Data are collected in “shots” comprising 60 s of transmitted waveforms and 10 s with the transmitter off to measure noise levels. The data quality is high, with a typical signal-to-noise ratio of ~100. This paper will present the results of a complete data analysis and preliminary 2D inversion of the data.